Fluorescent dyes have been produced from violanthrone (C.I. Vat Blue 20) and isoviolanthrone (C.I. Vat Violet 10), nine-ring aromatic diketone structures, by reductive alkylation with alkyl halides and zinc powder at elevated temperatures. These dyes fluoresce a green-yellow color. Complex apparatus may have a number of fluid lines; thus, it would be desirable to be able to differentiate by fluorescent dye color the source of a leak.
Also, the dyes may be used for tagging and identifying liquids, such as petroleum fuels. The availability of fluorescent dyes of a variety of hues increases the utility of such dyes for this purpose. Fluorescent dyes may be detected by apparatus described in U.S. Pat. No. 5,958,780, the teachings of which are incorporated herein by reference. Two fluorescent dyes which fluoresce at significantly different wavelength may be used in a binary tagging system which provides for an essentially unlimited number of identifying combinations.
Accordingly, it is a general object of the present invention to provide fluorescent dyes which fluoresce at wavelengths different from currently available fluorescent dyes.